The present invention relates to corrosion inhibitors for use with aqueous brines.
In many oil wells and gas wells, it may be desirable to contain the formation pressure by employing a hydrostatic head. This may be needed during the squeezing of sand consolidation compositions, during perforation operations, during well shut-ins, during gravel packing, or the like. Many well servicing fluids, sometimes referred to as completion or packer fluids, have been employed. These include, for example, drilling muds, brines, water, oil, ZnBr.sub.2 -CaBr.sub.2 solutions, CaCl.sub.2, CaBr.sub.2 or solutions and the like.
In recent years, deeper, high pressure and high temperature wells have resulted in a need for solids-free, well servicing fluids having higher densities than are currently available. This is particularly true of wells in the Gulf of Mexico (offshore Texas and Louisiana), where higher hydrostatic pressures often require well-servicing fluids having densities in excess of 15 pounds per gallon (ppg). The need for solids-free, higher density well-servicing fluids is met by brines which contain zinc salts, such as zinc halides.
High density brines and their preparations are set forth in U.S. Pat. No. 4,304,677 and U.S. Pat. No. 4,292,183. These zinc-containing brines have the disadvantage of being more corrosive than brines which are substantially free of zinc salts. Therefore, the high density brines, i.e., those brines having densities greater than about 14.5 ppg, are especially corrosive to oil well casings and equipment used in the service of said casings. The corrosion problem is exacerbated by the higher temperatures typically found in the deeper wells in which high density brines are used. Known corrosion inhibitors, such as film-forming amines, which have been used in high density brines do not provide adequate protection from corrosion at the higher temperatures associated with the deep wells in which high density brines typically are employed.
British Patent No. 2,027,686 is typical of the known technology in this area and discloses the use of sulfur compounds and quaternary pyridinium compounds as corrosion inhibitors.
It would therefore be desirable to develop a corrosion inhibitor which could provide increased protection for metals from corrosion caused by high density brines, especially by zinc salt containing high density brines at the higher temperatures found in deep wells.